fixes #1000 (#1043)

Author: martin-henz

xml/chapter3/section3/subsection3.xml

@@ -439,7 +439,7 @@ function insert(key_1, key_2, value, table) {
         set_tail(table,
                  pair(list(key_1, pair(key_2, value)), tail(table)));
     } else {
-        const record = assoc(key_2, tail(table));
+        const record = assoc(key_2, tail(subtable));
         if (is_undefined(record)) {
             set_tail(subtable,
                      pair(pair(key_2, value), tail(subtable)));